What Is Integration Testing? Definition, Basics, and Examples

Integration Testing

“The new software is apparently great but, when it has to fetch some data from the database or calls any other functionality, it starts malfunctioning.” What will you do if you hear about such experiences of your users?

These can create tremendously negative impressions about your product as well as of your business. And, you will be shocked to know that such mishaps are common if you do not focus on checking if the communication among different aspects of your app is working properly.

Your app has a lot of features and functionalities. Then it is natural that they will communicate internally to complete complex operations. But, this internal communication is not as simple as it may seem to be. It may easily experience the following issues -

  • Advanced features mean extremely complex sets of code running with dependencies on one another. And, that makes them extremely vulnerable to breaking down if they are not tested in every possible environment.
  • You are not building an app that will be used by one user at a time. Any popular app needs to deal with enormous traffic every moment. And, all those users may try to use all the functionalities in any random order. So, your product must be capable of handling its actions efficiently, or the app may easily crash.
  • Though by unit testing, it may be confirmed whether the small units are properly working as an individual part or not, it cannot be tested there if they perform the best collaboratively or not. That's where you will need integration testing.

Well, we are not here to scare you by mentioning the problems you may face by ignoring the collaboration between the units in your app.

We are here to make you aware of the simplest way of preventing those issues. Yes, we are talking about Integration Testing, the second phase in the testing pyramid, the universally followed best strategy for software testing.

What Is Integration Testing?

Integration testing is the process of checking how different software modules (also known as units) perform when they are connected together or dependent on each other. These tests determine if their compatibility is great and if they collaboratively perform with great efficiency as expected in the planning.

So, this testing process is all about connecting all the units together as one unit and testing the performance, functionalities, and reliability of the software.

That's why in the testing pyramid, this crucial phase comes after testing the small units in unit testing.

Why Is Integration Testing Important?

A question may arise if the unit tests are the largest subset of the whole testing process and if they hold such high importance, why Integration Testing became necessary. The following reasons can clearly state why unit tests are not enough to fulfill all your testing needs.

A module/unit is the smallest individual part of the software and multiple engineers develop these small pieces.

The thought/planning behind and the techniques used in the development of any particular unit may be completely different in another. And, unit tests can never check whether those units with different configurations have good compatibility among them or not.

  • It is a common scenario that the user requirements from the software change during the module development stage. So, naturally, those modules and the new requirements cannot be tested by unit testing. Then it becomes essential to test them through integration testing.
  • Unit tests often miss issues like data formatting, error trapping, etc. Missing to check parts like hardware interfaces, and third-party service interfaces is also a common scenario in unit testing.

As we can see that unit tests are not enough to ensure that the units that perform amazingly in isolation, can also perform at their best when integrated. That's where integration testing comes as a savior.

Advantages of Integration Testing

You saw why you need to perform integration tests but you must know its awesome advantages to make your concept more firm by making it mandatory in your test suite. So, let's go.

  • Integration tests ensure that the integrated modules are working as expected.
  • It allows you to start checking the compatibility of the modules with each other as soon as they are developed and tested through unit testing.
  • With integration tests, you can stay relaxed about the errors related to the interface between modules.
  • The modules need to interact with external APIs and other third-party tools. Integration testing ensures that they perform their best there.
  • It usually covers a larger volume of the system so, eventually the overall test efficiency increases.
  • Improved efficiency means naturally integration tests help you achieve a greater test coverage and you can experience a more reliable test suite.

Though conventionally software engineers or QA engineers perform the integration tests, amazing no-code testing tools like Preflight allow anyone from any department to easily create and execute efficient test cases. Let's explore more about this important testing phase in the next sections.

Difference Between Unit Testing and Integration Testing

Till now, you clearly got the idea that integration tests are a highly important part of an efficient test suite as unit tests are not enough to complete the objectives behind testing. Now, let's see the actual differences between those vital parts of the testing pyramid.

Unit Testing

Integration Testing

Primary working style is separately testing every small module/unit in isolation.

Primary working style is testing all the small software modules/units combinedly or when interconnected.

Checks if an individual unit is working properly without any dependency on another unit.

Checks if the units are working properly when they are interacting with each other or performing actions with dependencies.

Testers are completely aware of the software’s internal design.

Testers are unaware of the software’s internal design.

Unit testing is the first phase of the testing pyramid and is performed before any other test.

Integration testing is the second phase of the testing pyramid and is executed after unit testing and before system testing.

Unit testing is White Box testing.

Integration testing is Black Box testing.

Mostly developers perform these tests.

Mostly testers perform these tests.

Defects are easily identified.

Identifying defects is comparatively harder.

It costs less.

It costs comparatively more.

Types of Integration Testing

You got to know that integration testing means checking if the small software modules/units are performing at the best efficiency when they are interacting with each other for completing their operations. But, based on several parameters, Integration testing is also categorized into a few types that are mentioned below.

Big-Bang Integration Testing

As the name suggests, it is a type of integration testing that involves a huge volume. In this type of testing, when all the small modules are developed, they are integrated and tested in one go.

That's why these tests can only be performed when all components of the application are available to operate.

The point to remember is that due to the massive volume of these tests, they are only suitable for testing compact applications such as when the bundle has the entire software in it.


  • It's an amazing option for smaller systems.
  • You can execute these tests with very nominal planning.
  • It has a huge coverage that consists of almost every module.


  • Due to complicated fault localization, large-scale systems get exempted from the benefits of this type of testing.
  • As these tests need each and every module to be completely developed, the overall test suite becomes highly time-consuming.
  • Some modules often need extra attention while they are being tested. But, Big-Bang Integration testing involves testing all the modules at once. So, you become unable to prioritize critical modules differently.
  • This type of testing is not suitable for finding the root cause of problems.

Incremental Integration Testing

Incremental Integration testing is the name of the testing method where a test starts by connecting two or more modules that are logically related. Then more modules keep getting added and tested until all modules are integrated and the functionality is properly tested.

Based on the difference in the method of operation, this type of Integration testing is further categorized into three different approaches. Let's check them out.

Top-Down Integration Testing

This type of Integration testing follows a control flow hierarchy of testing the modules starting from the top-most ones and then gradually moving down to the lowest set of modules one by one.

One crucial point to keep in mind is that sometimes it may be possible that the lower-level modules might not have been developed while top modules are being tested.

Then the correcting approach is using stubs for those not ready modules because it provides the advantage of returning control to their superior modules in simple applications and in complex applications, they will simulate the full range of responses.

  • You can locate the faults easily.
  • You will get early access to prototyping.
  • You will get an extremely consistent test product.
  • Writing the stubs takes comparatively less time than the drivers.
  • Testing critical modules on priority reveal design faults earlier.
  • Several stubs are required.
  • There is a lack of attention to testing the lower-level modules.
  • You will get poor support for early release.
  • Testing of the basic functionalities occurs at the end of the cycle.

Bottom-Up Integration Testing

As the name suggests, it is the opposite of the Top-Down approach. Here you have to start with testing the lowest units first and then gradually move upwards. So, the testing follows the control flow from the bottom toward the upper phases.

Again, as it's the opposite approach of the top-down one, here it is possible that the higher-level modules may not be developed when the lower modules are tested.

In those cases, the functionality of missing modules is simulated by using drivers. The drivers are preferred because they perform numerous important tasks like invoking modules under test, passing test data, and receiving output data.

  • As it matches the control flow of the application, fault localization becomes much easier.
  • You can experience immense ease in creating the test conditions so no time is wasted getting started with this approach.
  • The eligibility to do development and testing together lets you meet customer specifications more efficiently.
  • It causes the top-level critical modules of the control flow of the application to be tested last.
  • You will require a lot of drivers in this approach.
  • The data flow is tested very late which eventually becomes a very inefficient thing.
  • You will never get the benefit of an early prototype.
  • Except only for the top-level modules, you need to create test drivers for modules at all levels. This massive need for drivers complicates test data management.
  • This approach has very poor support for early release.
  • Key defects between the interfaces are detected late.

Sandwich Integration Testing

We can see that both top-down and bottom-up approaches come with awesome advantages along with a few limitations. So, an efficient combination of those two approaches will do wonders in terms of overall test efficiency.

Hence, to cope with the limitations and get benefited by the advantages of both approaches, a hybrid approach of integration testing is used with the name “Sandwich Integration Testing” or “Mixed Integration Testing”.

The method of operation in this approach consists of viewing the system as three layers where the target layer is in the middle with one layer on the top and one at the bottom.

The top-down approach is used on the layers from the above to the middle and the bottom-up approach is used from the bottom layer to the middle.

The modules in the main target layer in the middle are tested with the highly prioritized Big-bang approach.

  • Makes you capable of performing both the top-down and bottom-up approaches in parallel or one after the other.
  • The amazing efficiency of this approach is tremendously beneficial for large enterprises and huge projects that further have several subprojects.
  • Combining two such extensive approaches turns out to be really expensive.
  • Being such a huge method exempts it from being suitable for smaller systems with huge interdependence between the modules.
  • It requires a huge team of numerous people with different skill sets at different levels.

These are the amazing Integration testing approaches that can let you check how the numerous small modules of your software are working when they are interacting with each other. And, after having a clear understanding of them from the above, you can easily decide which approach will work best for you.

Challenges That You May Face In Integration Testing

Though Integration testing is an extremely efficient top-level testing process, you may face some challenges while moving on with it. Here we are providing you with a brief of them for your better understanding.

  • Factors like databases, platforms, environment, etc. can sometimes make it difficult for you to manage integration tests.
  • If you are planning to integrate a new system into a legacy system or to integrate two legacy systems, know that it will involve a lot of testing effort and changes.
  • As integration testing may involve two different systems developed by two different companies, incompatibility between them can become a challenge for programmers.
  • Such a huge number of paths and permutations to apply for testing the integrated systems may cause huge confusion.

The Importance of Integration Testing

Despite a few challenges, Integration testing is an extremely important part of the widely popular testing pyramid that ensures that the small units in your application are working perfectly together.

Though this type of testing used to be a complex process, awesome no-code testing tools like Preflight have enabled everyone to conduct tests as a cup of tea. You can book a demo of this amazing tool now and experience the many benefits of integration testing!